Most bonsai information advises two safe periods in which the roots of plants are able to regenerate after being shortened. These times are listed as spring and autumn (fall). To the uninitiated this can be very misleading, resulting unfortunately with the death of their future bonsai. Some locations experience two growing seasons where summer dormancy is indicated by mature terminal leaves. At the end of this semi dormancy, terminal buds begin to enlarge but before the new leaf unfurls. This is the better way to explain the correct time for root-pruning rather than using seasonable terminology.
Within the Sydney region on roughly latitude 33 deg. S. the correct timing for pruning the roots of many plants is late summer & late winter repotting. This can still mislead as we have three varying degrees of temperatures in the greater metropolitan area, enough to make it slightly unsafe for some if we all repot on a given date. Many people sill repot in autumn ie. April, May. but may run into difficulty if the temps. fall dramatically before the roots have time to regenerate. As well we have some species that prefer to be root-pruned at the height of summer where they require continuing high temperatures to enable stress-free regeneration.
The weather in Sydney is unpredictable, making it difficult to know whether it will be safe to proceed with late summer root pruning. The determining factor for success is the guarantee of temp. stability. Regeneration will still take place where a slight increase in the spring and slight decrease in the autumn night temperatures for several weeks after. The object of this tip is to allow your plant to inform you when it is ready for its ‘little operation’.
Bonsai Koreshoff Nursery ©